With an endless number of apps now available to download on the Apple App Store and Google’s Play Store, reviews are used to keep the legitimacy of these apps. After you download and install an app, you can rate it out of five stars and write up a review detailing your thoughts. Review scores are aggregated and used to determine an overall score for the app. Unfortunately, this is sometimes skewed by the thriving trade in fake app store reviews.
There are a range of third-party services that can provide fake reviews offering to reach the top of the charts within your chosen category, however, it comes with serious consequences. This practice violates the Google Play Developer Program Policies and Apple’s App Store Review Guidelines. It can result in the removal of suspect reviews, the removal of the app, or even the expulsion of the developer from the program.

Make the necessary checks 

Check the reviews for every app you download – Fraudulent reviews will typically be one word or single-line comments providing a five-star rating. Ignore those completely. Look to the lengthier ones in-between these fake reviews.
Choose a trustworthy developer – If you’re using a third-party developer to create your app ensure you work with a genuine developer that doesn’t participate in this unethical behaviour – check their previous apps for anything suspicious.
Take reviews with a pinch of salt – Often users will only review the app to leave a negative review, therefore it is worth reading some of the reviews first to see what the issue is they are raising. Work with your developer to overcome the consistent problems to ethically improve your app store reviews.
Communicate with app reviewers – App stores now allow the developer to reply back to those that have left a review on your app. This allows you to get more information about a potential issue and engage with your users.
https://www.bbc.co.uk/news/technology-43907695
https://www.digitaltrends.com/android/can-you-really-trust-app-store-ratings/